The present invention relates generally to down-the-hole drill (DHD) hammers. In particular, the present invention relates to a pressure control check valve for a down-the-hole drill hammer.
Typical DHD hammers have a check valve and a fixed flow area within the DHD hammer. As such, the DHD hammer operates with working air volumes flowing through the fixed flow area within DHD hammer. Such fixed flow areas provide for adequate operation of the DHD hammer under normal dry conditions. Moreover, the filling and draining of working volumes within the DHD develop a pressure-flow characteristic that mimics a fixed orifice or port. However, DHD hammers often operate under “wet” conditions, e.g., when the drill hole is filled with water and the DHD hammer is submerged. Under such wet operating conditions, the wet conditions necessarily require the DHD hammer to operate under higher pressures to account for increases in outside pressures resulting from the wet operating conditions. To accommodate such wet operating conditions, the compressor used to supply feed air to the DHD hammer must supply higher working air pressures. However, typical compressors have a maximum operating pressure and when such maximum operating pressure is exceeded, the compressor must be adjusted to reduce its output air flow to compensate for the increases in outside pressures in order to most efficiently operate the DHD hammer. Without such adjustments to the compressor, conventional DHD hammers will not operate in its most efficient manner.
In other words, in down hole drill applications, especially deep holes where the presence of influx water is unknown, it would be desirable to perfectly match air consumption and pressure to the down hole drill to the capabilities of the power source. This ideal pairing would result in maximum down hole drilling performance. However, because the down hole drill must be setup for worst-case wet hole conditions operators do not have the ability to maximize performance for dry hole conditions which is normally drilled before wet zones are encountered. The problem is that when a drill hole becomes wet a much higher circulating pressure is needed and without adjustments to the down hole drill to reduce operating pressure, the pressure capacity of air compressors is exceeded and air flow must be reduced.
As such, a need exists for a DHD hammer than can address the foregoing limitations of conventional DHD hammers, e.g., a DHD hammer that adjusts its air flow depending on down hole pressure differentials so that as pressure increases within the hole, more air will be bypassed to manage compressor pressure. Such a need is satisfied by the DHD hammer of the present invention having a pressure control check valve.